<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>

    <button id="b">10</button>

    <script>
        
        var oBtn = document.getElementById('b') ;
        var flag = true ;
        oBtn.onclick = function() {
            if(flag) {
                flag = false ;
                var t = setInterval(function(){
                    oBtn.innerHTML--;
                    if(oBtn.innerHTML == 0) {
                        clearInterval(t);
                        flag = true ;
                        oBtn.innerHTML = 10 ;
                    }
                } , 500)
            }
        }

    </script>
    
</body>
</html>